Showing papers by "M. Omair Ahmad published in 2006"

Wavelet-based spatially adaptive method for despeckling SAR images

Abstract: In this paper, we introduce a new spatially adaptive homomorphic Bayesian wavelet-based method for despeckling synthetic aperture radar (SAR) images. The wavelet coefficients of the logarithmically transformed reflectance image and the speckle noise image are modeled using a symmetric normal inverse Gaussian prior and an additive white Gaussian noise distribution, respectively. These models are then exploited to develop a Bayesian maximum a posteriori estimator. A method is proposed for estimating the parameters of the assumed prior. The noise-free variance of a wavelet coefficient is locally estimated, and used in a minimum mean square error estimator to obtain the corresponding noise-free coefficient. Experiments are carried out on two synthetically speckled images and a real SAR image. The results show that the proposed method has a performance that is superior to that of the other existing methods in terms of the peak signal-to-noise ratio, ability to suppress the speckle in the homogeneous regions.

An Alternate Approach for Developing Higher Radix FFT Algorithms

Abstract: In this paper, the authors propose an alternate method to derive higher radix FFT algorithms by using a recursive approach and by appropriately combining the twiddle factors without increasing the structural complexity. Specifically, efficient radix-8 and radix-16 FFT algorithms are designed and their arithmetic complexities shown to be slightly less than those of the corresponding existing Cooley-Tukey FFT algorithms

New Radix- and Radix- DIF FFT Algorithms for 3-D DFT

Abstract: In this paper, new three-dimensional (3-D) radix- and radix- decimation-in-frequency (DIF) fast Fourier transform (FFT) algo- rithms are developed and their implementation schemes discussed. The algorithms are developed by introducing the radix-2/4 and radix-2/8 approaches in the computation of the 3-D DFT using the Kronecker product and appropriate index mappings. The butterflies of the proposed algorithms are characterized by simple closed-form expressions facilitating easy software or hardware implementations of the algorithms. Comparisons between the proposed algorithms and the existing 3-D radix- FFT algorithm are carried out showing that significant savings in terms of the number of arithmetic operations, data transfers, and twiddle factor evaluations or accesses to the lookup table can be achieved using the radix- DIF FFT algorithm over the radix- FFT algorithm. It is also established that further savings can be achieved by using the radix- DIF FFT algorithm. Index Terms—Radix-2/4, radix-2/8, three-dimensional (3-D) dis- crete Fourier transform (DFT), 3-D fast Fourier transform (FFT), 3-D radix- , 3-D radix- .

Novel techniques for reducing blocking artifacts in motion compensated frame

Abstract: We present two new techniques for reducing blocking artifacts in motion compensated frames. These techniques can be applied generally to motion compensated frames obtained by employing any partitioning schemes. In the first technique, the weighting coefficients of the overlapped block motion compensation are modeled with fuzzy relations. These fuzzy relations are formed based on two fuzzy sets, which define the closeness of a given pixel to the block boundaries in the horizontal and vertical directions, respectively. The second technique uses the similarity between a set of pixels inside a partitioned region and that on the borders to modify the border pixels. Simulations conducted on several benchmark video sequences indicate that the proposed techniques can improve the subjective quality of the frames as well as reduce the prediction error.